Pictures!

As I suspected the moment I come home everything grinds to a halt. But so you guys can see the robot as it stands currently I have taken a load of pictures to show exactly what is going into this robot.

This is the whole electronic system all wired up and working.

A Spektrum AR 6200, the Main and Remote receivers for the robot.

2x 7.2V 5100mAmp racing packs, these are wired in series to give 14.4V

One of the 4 drive motors, at maximum efficiency they produce 7720g/cm of torque!
 

The weapon drive motor, a Clash 15 racing motor which runs at 32'000 RPM at 7.2V,
but at 14.4 it doubles to a massive 64'000 RPM!

A Probe 12 speed controller for the Clash 15, this connects to the throttle mode on
the receiver to give me proportional control over the weapon speed.

The Sabertooth speed controller, parkBEC, receiver and Probe 12 all wired up together.

Completed Electronics!!!

Over the last 3 days since the last post I have managed to gather up all the final components required to complete the robots electronics! (Get in!)

I got the batteries, two 7.2V NiMH 5100mAh racing packs, a 30A speed controller for the weapon, which is intended to control the motor in large scale remote control cars, and a 31'000 RPM electric motor, for driving large remote control cars, from Antics. [Google it and its the first on the list]

I also got some unassembled packs battery connecters so that I could make the system easy to disassemble, a 20 tooth drive gear for the electric motor and a battery charger. On the way out I also popped into a lighting shop and got a rack of 30A connecting blocks. I had discovered the other day that I could not wire 2 20A cables into a single 20A block which meant that it was impossible to wire up the system given the number of splits I needed to do to get the power to the right places.

With all the parts I needed I went into uni and began wiring everything up. It took about 4 hours to tinn the ends of all the high amp cables, solder them to the appropriate connecting links and blocks and make sure that all the polarities were right. There was alos the fiddly time of trying to get a 30A gauge cable into the socket on the sabertooth, it was only big enough for about 2/3rds of the wire so I had to thin it there to get the cables in.

After binding the transmitter and receiver I wired up all the motors and the speed controller to the batteries and everything started jumping. Despite the transmitter with all its switches in the safe position the motors kept spinning at random back and forth. The drive motor for the weapon was linked to the throttle on the receiver and  immediately went to full power scaring the hell out of me. Well more than full power give it was meant to run at 32000 rpm at 7.2v but I was giving it twice that and as a result twice the speed. It makes a scary noise!

After turing everything off and taking a minute to chill out it turned out that the throttle safe was not a default on the transmitter explaining why the weapon motor had gone mad. But despite fiddling with the trim for the drive motors I could not stop them spinning totally, even after several rebinds.

Despite these problems, and the annoying fact that my supposedly infallible 2.4Ghz system was not as it claimed interference free, I had everything under some kind of control. With the safe switched on the weapon motor only started when I went past half way on the throttle and only went to full speed when I made it. The drive motor also did what they were supposed to as well, changing direction and turing at the correct speeds. There was a slight hiccup when I thought the the motors were drawing to much power for the sabertooth to cope with but it was only when it was doing it silly twitching thing and changing directions at full speed when it spiked. The first of which could be rectified totally and the other was just part of the system.

There was an even better moment when I moved the system onto the floor to take photos. The motors stopped twitching as much, down to almost nothing. It seemed that my infallible transmitter was being flummoxed by something inside he computers. Perhaps there dual 2.4Ghz processors, I don't know.

I will hopefully be uploading a video showing in detail the system and how everything is wired so that anyone else doing this wont have all the problems I had.

Next up is the chassis and attaching the wheels to the motors, which you would have thought would be simple but, no. The box section has been cut to length but due to the fact that I have done another redesign of the robots layout and the weapon's system it wont we welded before I have to go home.

The project may stall for the summer due to a lack of any tools or equipment or money but I should make some progress in various areas.

Progress!

It seems I am finally making some big(ish) steps towards starting construction on this machine. Along with cutting and sand blasting the last 3 parts for the base of the chassis,  I successfully tracked down, well I say tracked down, was told about is more accurate, a pair of speed controllers to drive the robots motors properly!

The device in question is a Sabertooth 2x12 RC. Dimension Engineering, the makers of the Sabertooth range, have obviously thought about the slightly more obscure uses there devices could be used for and have produced a speed controller (or ECU as it says on the packet) specifically for featherweight robots. The instruction leaflet says 'Sabertooth 2x12 RC is designed for combat robots from 16oz to 16lb, (13.6kg for us of the metric disposition, me included)' It has 2, 12 Amp speed controllers built into one small unit which is very handy and has bunch of features built in to make it more reliable make the robots easier to drive and keep itself from burning out. But possibly the biggest plus with this speed controller is that it is that it assumes that you are using it to do tank style steering, so rather than you having to fiddle around mixing the inputs and outputs on the transmitter you simply connect one cable to the Elevator channel on your receiver and the other to the Airleron channel. The onboard chip then interprets it for you and mixes it accordingly, all digital proportional of course. This one I got for a tad over £50, again from Technobots, which has also provided the next step.


It seemed sensible to just use one set of batteries on the robot rather than having separate power sources for the motors, receiver and weapons. BEC's or 'battery elimination circuits' were invented to do just that, well for the receiver anyway. The one that I went for was a ParkBEC 6V, again by Dimension Engineering and also from Technobots. The tiny little device siphons off power from the power going in and out of the ESC and takes it down from what ever you put in to 6V, this is then sent out again to the receiver. This little device cost £15 and saves on the annoyance of having to charge multiple batteries and having different chargers and also can save you on some crucial weight.


Both of these arrived today to add to the mounting pile of parts. Next on the list is the batteries and some high amp, multi-core wire for all the circuitry and from then things will actually start to move!!!

Money Makes The Wheels Go Round

As I mentioned before, this hobby is not cheap; there are so many expensive components that you cant just make yourself and most of them are liable to break the first time you enter the arena. I do know the basic principals behind robot electronics as in what bits you need, bare minimum, to get it to go and what each bit does but beyond that my knowledge is limited.


[At this point in time I do have quite a few parts and have learnt a lot since I started. I also have finally figured out the wiring arrangement for the robot to a certain degree and begun to solve the problem I mention at the bottom of this post. but progress is slow.]


I knew that I would need a transmitter and receiver, the bit that makes the robot remote controlled. Batteries, motors and wheels were obvious and I also knew that I would need some relays to control the night voltage motors with the low voltage receiver.


For the receiver I have brought a Spektrum DX6i transmitter and receiver set. Spektrum are one of the top manufactures of digital transmitters in the world and all there transmitters use a system called DSM 2. This is a very clever piece of tech which means that there is almost no interference and under 95% of circumstances there is none at all. This is now seen as standard for all combat robots above beetle weight for safety purposes but it is also the easiest to use and its fairly cheap to considering its advantages over the old 27 Mhz analogue transmitters.


The DX6i is Spektrum's lowest cost  transmitter with a digital mixing interface at around £135. There is the Spektrum DX5e at about £90, which is Spektrum's cheapest DSM 2 transmitter. This uses the  traditional array of front mounted switches to do the mixing. As a result it is cheaper and works perfectly well but for fine tuning the handling of the robot and full freedom over what controls what on the transmitter the DX6i is best.


The batteries are still posing a problem but I know that I want 2x 7.2v Nicad battery packs to run in parallel giving me 14.4 volts. I want the 14.4 volts to run the 4x RE 540/1 Metal Gearbox 50:1 motors. These operate at between 6v and 16v and draw around 0.2 amps each when loaded.


The wheels are currently 4x Treaded Rubber 101mm dia Wheels PK 2. I have yet to figure out how to attach them to the motors (I am going for a direct attachment onto the output shat as the motor incorporates its own gear box)


I have been quite lucky with the chassis. My university was replacing a load of old science lab desks. I got in there quick enough to ask them to give me two before they went off to the scrap-heap. The result is a 30mm, with 1.5mm wall thickness steel box section chassis which is very strong.


I also brought 3 Battle Switch relays to control each side of the robots drive train and the weapon. (Have now gone for a modified version of the 2nd Flipper/Spinner robot, without a flipper)


It seems right to tell you at this point how much this has all cost...


Just under £300.


If you go for the DX5e that drops to nearer £250 but its still a lot of money.


And now the crushing blow to my hopes. After talking it over with some electronics friends at university out turns out that the relays are all but useless to drive the robot. I can use one for the weapon but unless want the robot to 'handle worse than a school bus' I would need to by some kind of speed controller.


So today it has all ground to a halt once more until I can find a suitable pair of speed controler's.

1.1 Robotic Concepts and Robotic Indecision

As I have just said, nothing is ever as simple as it seems and even thinking about building a combat robot is hard enough on its own.


For those of you who were familiar with Robot Wars the diversity of the machines was incredible and even if 2 machines were similar they still operated and functioned very differently,, so picking a starting point for designing the robot was near impossible. I decide the best way to go about it was to draw down every design that entered my head then go through and dismiss the physically impractical ones and then again to remove the ridiculously expensive ones.


So after dismissing numerous mental designs, which included a full body spinner bases around 2 counter rotating planetary gear sets and a gigantic half conical crushing arm, I arrived at several plausible ideas. A wedge/flipper and spinning disc combination, a slightly different wedge/flipper and spinning disc combination, a full body hammer and lifting arm and another slightly different version of a full body hammer and lifting arm. (In short I did not have many options.)

Full Body Hammer Robot 1

Full Body Hammer Robot 2

 

Spinner Flipper Robot 1

Spinner Flipper Robot 2

 From the quick sketches I drew up some more accurate visualisations and from there I turned them into CAD models. It was at this point scale occurred to me. Solidworks demands the use of lengths and angles so obviously I had to pick some lengths to define the robot. The lengths determined size and a a result ,weight. 


Its probably a good idea at this moment to inform those of a non-robotwars background of the rules, specifically the weight categories which play a major role in what your machine is capable of. The full rules can be found here on the Fighting Robots Association (FRA) website.


http://www.fightingrobots.co.uk/documents/Build_Rules_2011.pdf


In summary the weight classes are Antweight [0 to 150 grams], Beetleweight [150 grams to 1.362kgs], Featherweight [1kg to 13.6kgs], Lightweight [12kgs to 27.5kgs, Middleweight [27.5kgs to 55kgs] ,Heavyweight [55kgs to 100kgs] and Super Heavyweight [100kgs to 145kgs].


Robotwars was mainly based around the Heavy weight category with a few fun incursions into the lower classes [If I recall correctly no super heavy weight fight has ever taken place in the british robot wars arena]. However the cost of building the heavier robots is considerably more than the smaller ones. If you are lucky with your purchase you can get an ant-weight in the box with a transmitter, for example 2 servos, receiver and the battery and that with a few modifications will serve you fairly well in an ant-weight fight. But the heavyweight ones cost a bomb! For example Chaos 2 is around £14'000, Wheeley Big Cheese is similar and Mortis was just over £30'000. Yes I know that some teams like 101 can famously build the whole robot for a pound and a penny but that is if you do this kind of thing for a living and have all the bits lying around.


For me the choice was fairly easy, Heavy weight and super heavy were far to expensive, middle and light had to few entrants to make it interesting and beetle weight and ant weight were to light to have fun with it.


Feather weight is a good place to start for most budding roboteers. Motors reasonably priced, the robot is small enough to cut down on expensive chassis materials, that old wheelbarrow rusting in the corner would make a good starting point for armour and you can even convert old windscreen wiper motors and wheel chair motors into drive motors if you can be asked.


But I digress...


With the weight limit established at 13.6Kg and a bit of maths later I worked out how big each of the chassis could be to take up 3.6kg of my weight limit. Each worked out to be between 0.5 and 0.4 of a meter long and 0.5 to 0.3 of a meter wide.


This is where things started to get expensive, well not for a short while anyway. With a size and weight established I now began to hunt down possible components for the robot and at the same time begin to buy everything Morrisons own brand if i was ever going to have money to spend on this machine.

1.0 In the beginning

A surprising amount has happened on this project before I began blogging it but it seemed sensible and helpful to begin. So far progress has been slow and steady but littered with frustrating mistakes and problems. But let me start at the beginning because otherwise none of this will make sense.

I have wanted to build a combat robot ever since Robot Wars burnt and bashed its way onto out TV screens some 13 years ago. But due to a lack of funds and an electronically and mechanically ignorant 7 year old brain it was always just a mad idea. The closes I have ever got until now was a Mini Robot Wars competition at a local engineering exhibition every year where lower secondary school students would build little machines to just shove the other around the arena with no real weapons. I leapt on this every time it came round but to no avail and most of the time the machine ended up getting shoved off the arena and breaking when it hit the floor. But by this point Robot Wars had been cut down and was no longer popular or cool to try and build fighting robots for some stupid reason.

I had pretty much given it up as a lost cause until about 5 months ago but after seeing the Gadget shows episode on combat robots I realized that Robot Wars still existed in some form or other. Since then I have been catching up on the latest developments in robotic combat and having it dawn on me that now I am at university with money of my own, and that real money not the £10 a month pocket money that I got from my parents*, that I might have a realistic chance of building a combat robot of my own.

But if I thought that it would now be relatively easy to just build a robot, I cant remember if i did or not, I was so wrong. Nothing is ever as simple as you think it is!

*Yes £10 is quite a lot but the transmitter alone is around £100 and to get to the stage I am now would take 30 months!